Continuous blood separators are used to separate whole human blood into its various components, such as platelets, red blood cells and/or plasma. These components are removed from the separators in separate streams, sometimes referred to as collect tubes. Normally, the collect tubes of the blood separator are continuously monitored to detect the undesirable occurrence of a spillover of one blood component into a collect tube intended to carry a different blood component. For example, the spillover of red blood cells into a collect tube intended to carry only platelets may be monitored.
A conventional technique by which undesirable spillover of red blood cells is monitored is the measurement of a color index of a non-red blood cell blood component that flows through a collect tube. This measurement is taken at a point downstream of the blood separator. By using a green light source and measuring the optical density of the non-red blood cell blood component, the total number of particles in the flowing non-red blood cell blood component and the green light absorbence of the non-red blood cell blood component can be monitored. An increase in green light absorbence in relation to optical density is then correlated to the occurrence of a red blood cell spillover.
This type of detection equipment typically requires a light source to be physically positioned on one side of a collect tube and a photosensor located on the opposite side of the collect tube. For this system to work in an optically efficiently manner, the portion of the collect tube adjacent the light source must present a generally flat surface to the light source and the photosensor. Relatively expensive schemes and custom containers have been used to produce a flat interface to the light source and to the photosensor, to thereby increase optical efficiency in this manner. For example, collect tubes may be flattened.
Another problem experienced with such detection equipment is that measurement of optical density requires measurement of the intensity of light that is received by the photosensor. Artifacts such as dirt particles that affect the light intensity received by the photosensor tend to provide a false indication of red blood cell spillover. In addition, there remains a continuous need for a detector equipment capable of greater sensitivity in a sensitive detection of red blood cell spillover.
The following United States patents are of general interest: U.S. Pat. No. 3,236,602 relates to a flow cell for the colorimetric examination of the light transmission characteristics of a liquid. U.S. Pat. No. 3,527,542 relates to apparatus for measuring blood flow wherein a first beam of monochromatic light passes through a cuvette to impinge on a first photocell while a second light beam impinges on a second photocell. The two photocell outputs are then compared. Reissue Pat. No. 29,141 describes a slit cell for use with optical particle sensors that operate on the principle of light scattering or interception.
Various patents identify light sources having particular wave lengths for the measurement of liquid characteristics. U.S. Pat. No. 4,227,814 describes an optical detector that is used with blood separating apparatus wherein red blood cell spillover is detected as a function of optical density. Low power light (750 foot candles at a power consumption of 1 to 2 watts) passes through the sample and a photodetector senses the optical density of the sample. Blue-green light 550 nanometers (nm) wavelength and a type 9 CAD sulfide photodetector are used. U.S. Pat. No. 4,229,179 describes spectrophotometric measuring apparatus wherein the visible, UV or fluorescent radiant energy that passes through a sample is detected. U.S. Pat. No. 4,444,498 describes the measurement of blood characteristics by using blood reflected light provided by two intermittently operating light sources having two different wavelengths (red and infra-red). Optical feedback loops control the intensity of the two light sources. A flat-bandwidth sensor detects the two reflections of different wavelengths.
Also by way of example, U.S. Pat. No. 4,810,090 describes the sensing of platelet concentration, and the detection of red blood cell spillover into the platelet flow, by using an infra-red-emitting LED (875 nm) and a green-emitting LED (565 nm) that operate at different times. These two LEDs emit light along an axis that extends through the stream of platelet flow. A first light sensor is placed on-axis and opposite the two light sources to detect light that passes on-axis and through the platelet stream. A second light sensor is placed generally across from the two light sources, but is located upstream of the first sensor, so as to measure light that is scattered off-axis and upstream of the two light sources. A third light sensor is placed generally across from the two light sources but is located downstream of the first sensor, to measure light that is scattered off-axis and downstream of the light sources. Under abnormal conditions, for example, when clumping, air bubbles, hemolysis, and spillovers of red blood cells or white blood cells has occurred, a color-index and a scatter-index are calculated.
Scattered light is also measured as a means of identifying blood components in other U.S. patents. For example, U.S. Pat. No. 4,522,494 describes an apparatus that determines the concentration of non-aggressive platelets and the concentration of discs that are within a flexible bag, using scattered laser light. U.S. Pat. No. 4,577,964 relates to the use of scattered light to discriminate platelets from red blood cells within a sample volume. U.S. Pat. No. 4,745,279 relates to the diffusion of infrared light by a volume of blood in order to measure the hematocrit of a volume of blood. This device may be used to measure oxygen saturation by the use of an LED light emitter and a reflection detector that are located on the same side of the blood volume. U.S. Pat. No. 5,372,136 describes a finger-clip/ear-lobe-clip arrangement in which at least two wavelengths of light are passed through body tissue and light transmission or reflection is detected by a photodetector.
While the prior art as exemplified above is generally useful for its limited intended purposes, the need remains for a construction and arrangement that provides a more sensitive detection of red blood cell spillover. In addition, there remains a need for equipment configuration wherein collect tubing does not have to be of special flattened construction manually between opposing transmitted and receiving devices.